Uplink and Downlink Chains

The term uplink chain is used to refer to the series of pieces of
equipment that are used to produce a radio frequency signal for sending out
data. The description provided here is imprecise as the exact configuration
can vary widely. The downlink chain is built using nearly the same
equipment in reverse order.

Take a look at the drawing below and note the path of devices on the left hand
side with all the up arrows.

DIGITAL
SATELLITE UPLINK CHAIN

How it works:

Digital data is sent to the modulator which takes the data and converts
it into a modulated signal in the Intermediate
Frequency range (70-140 Mhz). The modulators use standards such as
Digital Video Broadcast to organize communication over the microwave
link.

The Intermediate Frequency is piped to an "up converter"
(usually via shielded coaxial cable) which mixes the intermediate frequency
with a higher frequency to produce a final frequency which carries the modulated
data.

The final cleaned signal is transmitted down the wave guide to the dish.

The feed horn at the focal point of the dish emits the high frequency
radio transmission, which the dish focuses into a directional transmission
at the satellite.

Computer data is sent through a serial cable to a modulator. The modulator
takes the data and produces a radio freqency from it. This frequency is usually
in what is called the 'L-band' range (70-140Mhz). The modulator passes the information
over coaxial cable to an 'up converter', which converts the radio frequency
from 'L-band' up to microwave freqencies in the C, S, X, Ka, and Ku band ranges
(frequencies above 1,000 Mhz). Once the final signal has been produced, it's
amplified to increase its total effective output power. The signal is then sent
out a dish via the feed horn.